Every once in awhile, it’s fun to plot up the data and see what they look like. Lately, it’s been especially fun because our data set just keeps on growing and growing! Right now, we have 425 436 455 verified entries, 190 183 unverified, and around 30 20 10 in the double-check queue. We’ve also added a few new contributors this week, which is another nice bonus. Excellent progress, everyone!
MT III vs. Tibia Length (log mm); click for an enlarged view. Please forgive the color scheme - in the interest of time, the defaults were used.
This time, I decided to plot tibia length versus metatarsal III length for a variety of animals (at right; click on it for an enlarged version). As in one of our earlier plots of tibiae versus femora, ankylosaurs are weird. Their metatarsals are just really, really stubby relative to the tibiae (and the tibiae were really stubby relative to the femora). Interestingly, the saurischians in our sample seem to consistently plot above the ornithischians; in other words, saurischian metatarsals are long relative to the tibia (for the basal saurischians in our sample, at least).
Some analyses of mammals have suggested that a long MT III relative to the tibia may indicate more cursorial tendencies than for animals with a short MT III. Does this perhaps hold in dinosaurs? Were saurischians speedy, and ankylosaurs plodding? Or is there a phylogenetic effect that swamps any functional signal (as suggested for the mammal patterns by some authors)? Lots of additional analyses are needed.
The plot also shows a few gaps in our verified data set. Stegosaurs, basal thyreophorans, and pachycephalosaurs are not represented at all in this plot, because we don’t have any measurements of both a third metatarsal and a tibia for any members of these groups. If you’re looking for a data entry project, these would be excellent groups upon which to focus our efforts.
Do you want to do your own analysis? You can! All of the data used to create the plot above are publicly available.
The Open Dinosaur Project 
Well, ankylosaurs probably were pretty slow… they certainly don’t look built for speed! And they would have no use for it, as well-defended herbivores (no need to chase down prey or flee). So that seems like a positive sign.
Basal saurischians were mostly small and fairly gracile. Perhaps looking at big sauropods would tell whether it’s a phylogenetic thing, a feature of saurischians, or a feature of the body type common to basal saurischians?
That’s a beautiful plot!
Questions:
(1) What spp are represented in “Saurischians”? Bipeds or with quadrupeds?
(2) What role does “size” play? What would a plot of juvenile hadrosaurs show?
(3) From Q2, it seems that at a smaller size, a higher MT III:titia ratio (roughly, cursoriality} is necesary to attain an equivalent absolute speed of a larger animal (e.g. prey), in which a longer stride already helped.
(4) At least one separate line of evidence may substantaite that this Saurischian data is genuine: the footprint length to hip height ratio (e.g. Thulborn, 1990)
Hadrosaur metatarsals are extremely interesting… could you by any chance make a graph of the Tibia: MT III ratio vs. the Humerus: MC III ratio next?
Well, at least vaguely interesting. 😉
I will measure some of our Stegosaur material this week at the museum and post it. I can’t remember if we have a tibia or not…
That would be fantastic! The more stegosaurs, the better.
1) Mostly bipeds (Coelophysis, Herrarasaurus, Eoraptor).
2) Good question.
3) Hmm. . .interesting suggestion. I would bet there’s something in the modern comparative literature relevant to this topic.
4) Time for the Open Footprint Project!
Maybe that will be our next plot!
Indeed. Right now, we’re mainly including saurichians for an outgroup (i.e., seeing what the basal condition for dinosaurs is). It would be interesting if ornithischians were characterized by a change in body proportions early on.
Me, I’m goggling at the vacuum of specimens with tibiae around 10^2.8, or roughly 700 mm. What can it mean?
It looks like ornithopods resist entering it from the low end, and hadrosaurs hurry past it. Or maybe animals of such dimension are invulnerable, and the samples we have are from those that failed to achieve it, or overshot it, and died.
There is at least 3 possible scenerios to Nathan’s observation 🙂
(1) We have a genuine lack of data (no fossil, or no entry of data).
(2) We have a case of punctuated equilibrium: a relatively rapid evolutionary increment of size in Euornithopoda.
(3) We have a case of high adolescent mortality. Dinosaurs could be perceived as a mixed K-r stretagist with high birth rate (thus an abundance of juvenile hadrosaur samples) AND some parental care. Once this care ends (post-yearlings) the mortality rate shot up. Those surviving would however live long enough to give us ample adult fossils as well.
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